Actually for row C, this is a better formula to use:

=IF(ISERROR(INDEX($A$1:$A$1000,SMALL(IF($B$1:$B$10 00="Duplicate",ROW($B$1:$B$1000)),ROW(1:1)))),"",I NDEX($A$1:$A$1000,SMALL(IF($B$1:$B$1000="Duplicate ",ROW($B$1:$B$1000)),ROW(1:1))))

Just paste it, hold down Conrol and Shift and then hit enter, and then
release all 3 buttons. When it works, there will be {} around the entire
formula.
Copy down.